1. Field of the Invention
The present invention concerns a device for portable tools with internal combustion engines ensuring the instantaneous, automatic stopping of the operation of the latter after sudden and violent movements to which they are exposed during their use, in order to ensure the user's safety. It applies in particular to chain saws with internal combustion engines.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Official regulations require chain saws to be equipped with a safety device ensuring the stopping of the tool in the event of a strong recoil or “kick back” as professionals call it and which corresponds to an acceleration expressed in m/s2 (between 700 and 2000 m/s2, depending on the type of tool).
At present, in chain saw applications, this device consists most often of a mechanical means which covers the front handle and which, either by inertia tied to the kick back or by striking the hand holding this handle during a violent acceleration, activates a system which brakes the drive of the cutting chain until the engine of the tool stops.
A comparable device is described for instance in the EP-1350607 document.
These safety devices consisting of mechanical means present however several drawbacks: they function only through inertia when the tool is held with only one hand; they work only in a single plane (forward/backward) and do not function in the other planes; they can, in case of a violent kick back, cause injuries due to the shocks on the hand in contact with the device; their trip point through inertia is very high due to the fact that the masses in motion are very small (between 700 and 2000 m/s2, depending on the type of tools); their response time is relatively slow (in the range of 10 to 15 milliseconds); their sensitivity is not adjustable; they function by action on the tool properly speaking (for example on the chain in the chain saw application); they are subject to wear due to friction; they can become blocked in the off-position; and they are relatively bulky and expensive.
In documents US-2004/0181951 and US-2007/0008162 are described portable electric tools equipped with a safety system consisting of accelerometers on three axes capable of commanding the operations of said portable electrical tools to stop, via a logic circuit when a predetermined trip point of acceleration has been reached. These safety systems are not applicable to portable tools with internal combustion engines such as chain saws.